The director of the American Central Intelligence Agency says Osama bin Laden's al-Qaeda network is planning more attacks against the United States and its allies.

George Tenet told a US Senate committee that al-Qaeda remained the most serious and immediate threat facing the country.

Al-Qaeda leaders still at large are working to reconstitute the organisation and resume its terrorist operations, we must be prepared for a long war

George Tenet

He said that the US should be prepared for a "long war", adding that al-Qaeda had not been destroyed.

"Al-Qaeda leaders still at large are working to reconstitute the organisation and resume its terrorist operations," he said.

"We must be prepared for a long war, and we must not falter."

Nearly 1,000 people in more than 60 countries have been arrested on suspicion of having links with al-Qaeda, which has been blamed for the 11 September attacks on New York and Washington.

The network might plan attacks on the Winter Olympics - due to begin in Salt Lake City at the weekend - as well as US and allied targets around the world, Mr Tenet said.

Al-Qaeda is likely to continue using conventional weapons - but is also trying to acquire chemical and biological weapons, he added.

Bin Laden fate unknown

Mr Tenet said the network was thought to be trying to build a so-called dirty bomb, adding that he thought some "tactical co-operation" was possible with Iraqi leader Saddam Hussein.

Tenet does not know if Bin Laden is alive

Mr Tenet said he did not know if Bin Laden himself was alive but believed that Taleban leader Mullah Mohammad Omar was.

The CIA director would not discuss any more details about the whereabouts of the two men - the two most wanted in the war against terror - in the open session of the committee hearing.

But when asked by Senator Pat Roberts why the CIA could not get close to Bin Laden, he suggested that an agent had, but refused to elaborate in open session.

More threats

BBC Washington correspondent Tim Franks says Mr Tenet drew on the tradition that the CIA director sees threats and dangers everywhere, and in the process appeared to win approval from some of the most senior decision-makers in American politics.

Mr Tenet went on to reinforce President George W Bush's assertion that North Korea, Iran and Iraq were the world's most menacing countries.

And he warned that Russia and China were trying to win money and influence by exporting weapons technology to them.

The committee is scheduled to hold a closed hearing later on Wednesday.